The heat capacity of water swollen poly(2-hydroxyethyl acrylate) above and below 0 °C

Abstract

The heat capacities of water swollen poly(2-hydroxyethyl acrylate) were determined with a DSC-2 calorimeter in the range 220-350 K for concentrations between 0 and 1.95 g water per 1 g polymer. The results confirm conclusions obtained in a preceding paper for the system poly[2-(2-hydroxyethoxy)ethyl methacrylate]-water. At temperatures above 0°C the partial specific heat capacity of water in the polymer is independent of composition and equal to the specific heat capacity of pure liquid water. This indicates that water sorbed in the polymer is not strongly bound. Analysis of data on the heat capacity below 0°C has led to a conclusion that at a water content below 0.2 g/g or at temperatures 230 K and lower, the crystallization of water from the gel is inhibited by factors which make impossible the attainment of thermodynamic equilibrium. Non-freezing water should not be identified with strongly bound water.